This continuing microelectrode study is concerned with the important question of the influence of interoceptive systems on unit activity of the forebrain. The experiments are performed on gently restrained sitting squirrel monkeys with chronically implanted electrodes next to the vagus nerve in the jugular fossa. This past year's work has provided a further characterization of units in the putamen and frontotemporal portion of the limbic system that are responsive to vagal volleys. Of particular interest was the finding of units in the limen insula, claustrum, anterior amygdala, and putamen that appeared to discharge in connection with respiration and that could be entrained by vagal volleys. BIBLIOGRAPHIC REFERENCES: Bachman, D.S., Hallowitz, R.A., and MacLean, P.D.: Effect of vagal volleys on serotonin on units of cingulate cortex in monkeys. Brain Research, 130: pp. 253-269, 1977. Radna, R.J. and Vaughn, W.J.: CAUDAR: Computer Assisted Unit Data Acquisition/Reduction, National Technical Information Service, Report Number NIH/DB-77/003, 1977.